In recent years, as a projection optical system for a projector which can perform projection from a short distance so as to obtain a large picture plane, a projection optical system using a refraction optical system and a concave mirror is proposed (see PTLs 1 and 2, or the like).
However, for example, in PTL 1 (JP-A-2006-235516), a significantly wide angle of view is realized using the refraction optical system and the concave mirror, a curved mirror is enormously large in size, and the entire length of the mirror is significantly increased. In addition, in PTL 2 (JP-A-2007-079524), for example, the angle of view is about 60 degrees in an eighth example, and a combination of a concave mirror and a convex mirror allows the mirror size to be decreased. However, similar to PTL 1 described above, the entire length needs to be significantly increased. In addition, the two mirrors in this configuration have aspheric surfaces, respectively, and thus it is highly difficult to manufacture the mirrors in terms of achieving accuracy and assembly.
As described above, in a complex optical system including the refraction optical system and the concave mirror, an ultra-wide angle of view is obtained, but it is difficult to decrease the entire length. Therefore, the complex optical system is not suitable for equipment such as a front projector in which portability is important.